(i) Field of Invention
This invention relates generally to improved poly(butylene terephthalate) polymer based molding resins for making components for use in metallic electrical assemblies in an elevated temperature environment. Such components are typically prepared from so-called "flame retardant" molding compositions. More particularly, it relates to flame retardant molding resins for making components having reduced tendency to corrode a copper surface exposed to a common unventilated atmosphere at ambient temperatures within the range 100.degree. C. to 180.degree. C. The components are prepared from flame retardant halogen-containing molding compositions that contain defined amounts of an alkylhydroxyphenylalkanoylhydrazine. The invention also relates to the molding process; the molded less corrosive component; and the eletrical equipment containing such components.
(ii) Prior Art
Components prepared from flame retardant molding resins containing at least 50 weight percent poly(1,4-butylene terephthalate) based polymer and aromatic halogen groups, have been widely used in metallic electrical assemblies in unventilated environments at elevated temperatures below 100.degree. C. However, electrical equipment manufacturers have been hesitant to utilize the same components in new electrical applications wherein the elevated temperature environment is within the range from 120.degree. C. to about 150.degree. C., because of fear of corrosion to fine metal electronic parts having surfaces not in direct contact with the polymer. Such new applications include for example telephone connector assemblies that are compact and carry high currents.
Bell Telephone Laboratories has developed a screening test for predicting the suitability of a given molding composition for such applications. The test is fully described hereinafter in Example 3.
U.S. Pat. No. 4,104,242 (Kochanowski et al.), Example 1, exemplifies molded articles comprising poly(1,4-butylene terephthalate), commonly known as PBT, and N,N'-bis(3,5-ditert-butyl-4-hydroxyhydrocinnamoyl)-hydrazine (Ciba-Geigy Corporation, Irganox.RTM. MD-1024). The articles had improved "long term (high) voltage breakdown resistance", when tested in the form of rotors for distributors of automotive ignition systems. Nowhere does the patent refer to the corrosion rate of the metallic portion of the rotor and/or distributor. The Example does not use a flame retardant composition, although elsewhere it is stated that the molding powder formulations may contain flame retardants etc (column 5, lines 55-58). The Example does not state the temperature reached by the rotor in the test, but it was presumably quite low since rotors can be readily removed from hot automobile engines without the use of gloves.
Ciba-Geigy's product bulletin "Irganox.RTM. MD-1024" (undated) described MD-1024 as a metal deactivator and antioxidant which when incorporated into polymeric materials such as polyolefins and nylons will prevent failure of the polymer when these materials are used as insulation in direct contact with metals, such as copper. The bulletin does not specifically refer to polyesters. It often recommends the use of Irganox 1010 (a high performance phenolic antioxidant that is free of nitrogen) in conjunction with Irganox.RTM. MD-1024.
In FIG. 2 of the product bulletin, increasing the concentration of blends of Irganox.RTM. MD-1024 and Irganox.RTM. 1010, up to 0.8%, clearly shows a nearly directly linear increase in stabilizer performance. The product bulletin also teaches that "(i)t is also expected that Irganox.RTM. MD-1024 may have utility in deactivating titanium and other metal catalyst residue present in polyolefins and other polymers, thereby improving end-use thermal and light stability." The bulletin further cites two patents (both assigned to Ciba-Geigy): U.S. Pat. Nos. 3,660,438 and 3,773,722.
U.S. Pat. No. 3,660,438 discloses alkylhydroxyphenylalkanoyl-hydrazines as stabilizers against oxidative and/or thermal degradation for organic materials. (Column 1, lines 35-38). Examples of organic materials are listed as: vinyl resins, vinyl esters, butadienes, styrenes, polyolefins, polyurethanes, polyamides, polyacetals and polyesters, such as polyethylene terephthalate. The claims of the '438 patent are directed to the compound - alkylhydroxyphenylalkanoyl hydrazine.
U.S. Pat. No. 3,773,772 is a divisional of the '438 patent and discloses identical subject matter. The claims of the '722 patent are directed to the composition comprising polymeric materials with up to 5% of an alkylhydroxyphenylalkanoyl hydrazine compound as a stabilizer.
U.S. Pat. No. 3,888,824 is a continuation-in-part of the '438 patent and is of general interest in that it discloses an alkylhydroxyphenyl alkanoylhydrazine for the stabilization of polyesters such as polyethylene terephthalate (Column 4, lines 28-29).